Low-k SiC copper diffusion barrier films

ABSTRACT

Copper diffusion barrier films having low dielectric constants are suitable for a variety of copper/inter-metal dielectric integration schemes. Copper diffusion barrier films in accordance with the invention are composed of one or more layers of silicon carbide, at least one of the silicon carbide layers having a composition of at least 40% carbon (C), for example, between about 45 and 60% carbon (C). The films&#39; high carbon-content layer will have a composition wherein the ratio of C to Si is greater than 2:1; or &gt;3:1; or &gt;4:1; or &gt;5.1. The high carbon-content copper diffusion barrier films have a reduced effective k relative to conventional barrier materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/869,474filed Jun. 15, 2004 now U.S. Pat. No. 7,282,438 and titled LOW-K SICCOPPER DIFFUSION BARRIER FILMS. The disclosure of this prior applicationis incorporated by reference herein in its entirety and for allpurposes.

BACKGROUND

This invention relates to low dielectric constant layers for use invarious applications. The invention also relates to methods of forminglow dielectric constant layers in a wide range of VLSI and ULSIfabrication operations.

As the features of microelectronic integrated circuits devices arereduced to smaller sizes, the electrical properties of the materialsthat constitute the devices will require change and improvement. Onematerial that must be improved is the electrical insulator(“dielectric”) used between the wires, metal lines, and other elementsof the circuit. Without improvement in the insulator material, therewill be increased problems due to capacitive effects such as coupling(crosstalk) and propagation delay. The speed at which future circuitswill operate will be limited by RC delay in the interconnect.

These difficulties can be mitigated by preparing the circuit using aninter-layer dielectric (“ILD”), for example an inter-metal dielectric(“IMD”), having a dielectric constant that is as low as possible. Theintegration of Cu metal and IMD with a low dielectric constant continuesto challenge the integrated circuit industry as device size and wiringdimensions are scaled down. Low dielectric constant (k) (“low-k”),insulators, with k significantly lower than that of presently used SiO₂(3.9), are needed for reducing capacitive coupling and improvingswitching performance of future ULSI circuits. In this regard, theeffective dielectric constant (k_(eff)) encountered by the signal in theinterconnect structure is the most important parameter.

Cu/IMD integration schemes typically involve the incorporation of othermaterials along with the bulk inter-metal dielectric material, forming astack. These other materials may include copper diffusion barrier,copper capping layer and hardmask (e.g., CMP and etch stop) materialsneeded to prevent copper poisoning of the bulk low-k dielectric, toprotect the relatively soft low-k dielectric, and to facilitate theDamascene processing used in the device fabrication. These materialshave a substantial impact on the effective k of the IMD stack. Thus, theIMD must meet the dual challenges of minimizing the effective k of thestack while providing material selectivity with the use of reduced ketch stop, barrier and capping materials.

Silicon nitride (SiN) provides a film having satisfactory properties asa copper diffusion barrier, but its dielectric constant is relativelyhigh. A recently developed PECVD SiC dielectric barrier is a promisingcandidate to replace SiN in many copper barrier applications because ofits relatively low dielectric constant (k<4.5). However, existing PECVDSiC technology has shown limitations in achieving dielectric constantslower than 4.5 while continuing to maintain other integrationrequirements relating to line to line leakage, via poisoning, etchselectivity, Cu hillock formation and atmospheric moisture uptake.Improved materials and processing are required.

SUMMARY OF THE INVENTION

The present invention is mainly directed to copper diffusion barrierfilms having low dielectric constants suitable for a variety ofcopper/inter-metal dielectric integration schemes, and methods of makingand using them in semiconductor devices. Copper diffusion barrier filmsin accordance with the invention are composed of one or more layers ofsilicon carbide, at least one of the silicon carbide layers having acomposition of at least 40% carbon (C), for example, between about 45and 60% carbon (C). The films' high carbon-content layer will have acomposition wherein the ratio of C to Si is greater than 2:1; or >3:1;or >4:1; or >5.1. The copper diffusion barrier films maintain aneffective dielectric constant of between about 2.8 and 3.9 in thepresence of atmospheric moisture.

The copper diffusion barrier films of the invention may be composed of asingle silicon carbide layer. According to this embodiment, a layer ofundoped silicon carbide with a dielectric constant lower than 4, or evenas low as 3 or lower, may be deposited as a copper diffusion barrier.Alternatively, the copper diffusion barrier films may be composed ofmultiple layers of silicon carbide having different compositions with alow effective dielectric constant, lower than 4 for example. The copperdiffusion barrier film may have a thickness in the range of about 20 Åto 2000 Å.

In multi-layer copper diffusion barrier films of the invention, thecomposition of the layers may be tailored to provide additionalfunctionality to the copper diffusion barrier film, and therefore to anIMD in which the copper diffusion barrier is incorporated. For example,nitrogen-doped silicon carbide and/or oxygen-doped silicon carbidelayers may be incorporated into copper diffusion barrier film bi- ortri-layer stacks with undoped silicon carbide in accordance with thepresent invention to confer enhanced etch selectivity and moistureabsorption blocking, respectively. While the dielectric constants of theindividual oxygen- and, particularly, nitrogen-doped silicon carbidelayers may be greater than 4, the much lower dielectric constant of theundoped silicon carbide portion of the barrier film can bring itsoverall k (effective k, k_(eff)) down below 4. In this way, theinvention provides effective low-k IMD/Cu integration schemes.

Low-k copper diffusion barrier films in accordance with the inventionmay be formed by PECVD processes using relatively high carbon (C)content organosilicon precursors not previously used in thisapplication. Precursors having a carbon composition of at least 40%, forexample, between about 45 and 60% carbon (C) may be used. Suitableprecursors may have at least 45%, 50% or 55% C and ratios of C:Si of atleast 2:1 and as high as 5:1, or higher. In particular, organosiliconprecursors such as ethynyltrimethylsilane, vinylphenylmethylsilane andphenyldimethylsilane, among others, may be used.

Other embodiments of the invention include a wholly or partiallyfabricated semiconductor device. The device includes a metalinterconnect formed substantially of copper and a copper diffusionbarrier adjacent the metal interconnect. The copper diffusion barrier iscomposed of one or more layers of silicon carbide, at least one of thesilicon carbide layers having a composition of at least 40% carbon (C)and/or ratios of C:Si of at least 2:1 and as high as 5:1, or higher, asnoted above. In some such devices, the copper diffusion barrier film maybe composed of a single silicon carbide layer. In other such devices,the copper diffusion barrier films may be composed of multiple layers ofsilicon carbide having different compositions arranged to achieveeffective low-k IMD/Cu integration schemes, as noted above.

Some aspects of the invention provide a method of forming at least aportion of a semiconductor device. The method includes the followingoperations: forming a trench in a first dielectric layer; forming acopper interconnect in the trench; and forming a copper diffusionbarrier film on the copper interconnect, the copper diffusion barrierfilm comprising one or more layers of silicon carbide, at least one ofthe silicon carbide layers having a composition of at least 40% carbon(C) and/or ratios of C:Si of at least 2:1 and as high as 5:1, or higher,as noted above.

The step of forming a copper diffusion barrier film involves aplasma-enhanced chemical vapor deposition (“PECVD”) process using one ormore high carbon-content organosilicon precursor gases. The PECVDprocess may be performed in standard PECVD apparatus.

These and other features and advantages of the present invention will bedescribed in more detail below with reference to the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a copper diffusion barrier film in accordance with anembodiment of the present invention.

FIGS. 2A-E illustrate various configurations of copper diffusion barrierfilms in accordance with the present invention.

FIG. 3 is a plot of the results of a simulation conducted to determinethe effective dielectric constant of various bi-layer copper diffusionbarrier films in accordance with the present invention.

FIG. 4 is a plot of the relationship between as-deposited and actualdielectric constant (k drift) and stress drift for undoped siliconcarbide copper diffusion barrier films deposited using differentprecursors in accordance with the present invention.

DETAILED DESCRIPTION

In the following description, the invention is presented in terms ofcertain specific compositions, configurations, and processes to helpexplain how it may be practiced. The invention is not limited to thesespecific embodiments. Examples of specific embodiments of the inventionare illustrated in the accompanying drawings. While the invention willbe described in conjunction with these specific embodiments, it will beunderstood that it is not intended to limit the invention to suchspecific embodiments. On the contrary, it is intended to coveralternatives, modifications, and equivalents as may be included withinthe scope and equivalents of the appended claims. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. The present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process operations have not been described indetail in order not to unnecessarily obscure the present invention.

Introduction

The present invention is mainly directed to copper diffusion barrierfilms having low dielectric constants suitable for a variety ofcopper/inter-metal dielectric integration schemes, and methods of makingand using them in semiconductor devices. Copper diffusion barrier filmsin accordance with the invention are composed of one or more layers ofsilicon carbide, at least one of the silicon carbide layers having arelatively carbon-rich composition of at least 40% carbon (C), forexample, between about 45 and 60% carbon (C). The films' highcarbon-content layer will have a composition wherein the ratio of C toSi is greater than 2:1; or >3:1; or >4:1; or >5.1. In preferredembodiments, the copper diffusion barrier films maintain an effectivedielectric constant of between about 2.8 and 3.9 in the presence ofatmospheric moisture.

The term “semiconductor device” as used herein refers to any deviceformed on a semiconductor substrate or any device possessing asemiconductor material. In many cases, a semiconductor deviceparticipates in electronic logic or memory, or in energy conversion. Theterm “semiconductor device” subsumes partially fabricated devices (suchas partially fabricated integrated circuits) as well as completeddevices available for sale or installed in particular apparatus. Inshort, a semiconductor device may exist at any state of manufacture thatemploys a method of this invention or possesses a structure of thisinvention.

The copper diffusion barrier films of the invention may be composed of asingle silicon carbide layer. Alternatively, the copper diffusionbarrier films may be composed of multiple layers of silicon carbidehaving different compositions. Low-k copper diffusion barrier films maybe formed by PECVD processes using novel organosilicon precursors notpreviously used in this application. In particular, organosiliconprecursors such as ethynyltrimethylsilane, vinylphenylmethylsilane andphenyldimethylsilane, among others, may be used to achieve a barrierlayer with a k as low as 3, or lower. In one embodiment, a layer ofundoped silicon carbide with a dielectric constant lower than 4, or evenas low as 3 or lower, may be deposited as a copper diffusion barrier.Alternatively, the copper diffusion barrier films may be composed ofmultiple layers of silicon carbide having different compositions with ais low effective dielectric constant, lower than 4 for example.

Barrier Films and Integration Schemes

The copper diffusion barrier films of the invention may be composed of asingle silicon carbide layer. According to this embodiment, a layer ofundoped silicon carbide with a dielectric constant as low as 3 may bedeposited as a copper diffusion barrier. The copper diffusion barrierfilm may have a thickness in the range of about 20 Å to 2000 Å.

Crystalline SiC has a dielectric constant of >9.0 and the covalent Si—Cbond can break very easily at high temperature leading to high leakage.However, excess hydrogen in PECVD deposited SiC films maintainsdiscontinuity in the Si—C bonds and hence eliminates the leakage currentproblem at higher temperature and decreases the dielectric constant ofPECVD deposited SiC films. Moreover, it has been discovered that low-kcopper diffusion barrier films (e.g., undoped films with k less thanabout 3.6 (lower than that achievable using tetramethylsilane as aprecursor) and as low as 3 or lower; and multilayer films with k_(eff)less than 4 in many cases) may be formed by PECVD processes usingcarbon-rich organosilicon precursors not previously used in thisapplication. In particular, organosilicon precursors such asethynyltrimethylsilane, vinylphenylmethylsilane, phenyldimethylsilane,tri-iso-propylsilane, 3-(trimethylsilyl)cyclopentene,vinylphenyldimethylsilane and vinyldimethylsilane may be used.

Table 1 shows compositional data and the respective dielectric constantsof various doped (oxygen-doped SiC (ODC); nitrogen-doped SiC (NDC)) andundoped silicon carbide (UDC) layers deposited using differentprecursors: tetramethysilane (MS); ethynyltrimethylsilane (ETMS),vinylphenylmethylsilane (VPMS) and phenyldimethylsilane (DMPS). NDC hasa composition of Si, C, N and H. ODC has a composition of Si, C, O, H,while UDC has a composition of Si, C, and H.

TABLE 1 Film composition and k values of UDC, NDC, and ODC depending onprecursors. Sample Si N H O C Dielectric constant (k) 4MS_UDC 0.24~0.260 0.38~0.4  0~0.03 0.30~0.37 3.6~4.0 ETMS_UDC 0.11~0.17 0 0.32~0.4 0~0.04 0.45 2.8~3.6 VPMS_UDC 0.09~0.11 0 0.32~0.34 0~0.02 0.54~0.563.0~3.6 DMPS_UDC 0.09~0.12 0 0.32~0.36 0~0.03 0.52~0.54 2.9~3.3 4MS_ODC0.26 0 0.24 0.2 0.3  4.4 4MS_NDC 0.26 0.24 0.24 0 0.26 5.2As the table shows, the precursors having at least 40% carbon (C), forexample, between about 45 and 60% C (ETMS, VPMS and DMPS) produceundoped films having that same proportion of carbon which have adielectric constant significantly lower than that of films formed withthe conventional tetramethylsilane (4MS) precursor. While not shown inthe table, the same is true for the doped variants using the highC-content precursors.

Barrier films in accordance with the invention are formed from thesehigh carbon-content precursor materials in various configurations. Thefilms will generally have at least one high carbon-content layer with acomposition wherein the ratio of C to Si is greater than 2:1; or >3:1;or >4:1; or >5.1. Undoped and doped films formed from these materialsprovide improved performance as copper diffusion barrier films (and etchstops) over their conventional analogs as a result of their lowerdielectric constants.

For example, undoped silicon carbide (UDC) barrier films deposited withthese high carbon-content precursors have much lower k values andexhibit better etch selectivity to the via/line dielectric film due tothe higher carbon content. These layers thus provide improvedperformance as copper diffusion barrier films (and etch stops) overconventional undoped films. FIG. 1 shows an example of a single layerbarrier film 101 disposed on the surface of a copper layer 103, such asa metal line or via, in order to provide some context for how the filmwould be disposed when used in a semiconductor device. The film iscomposed of a layer of high C-content UDC 105 on the copper 103. Such afilm may have a k as low as 3, or lower.

Moreover, the advantageous properties of doped SiC materials can beleveraged in accordance with the present invention to provide low-kcopper barrier films with enhanced performance. In this regard, UDC isvery low k and provides good etch selectivity, ODC layers block moistureabsorption and NDC enhances etch selectivity. Amine free UDC and ODCprocessing can eliminate via poisoning caused by amine contamination ofthe low k material during damascene processing These layers, one or moreof which having high carbon-content (and corresponding low-k) may becombined in a variety of configurations to form multi-layer,multi-functional (e.g., copper barrier, etch and/or CMP stop, moisturebarrier) SiC barrier films depending on the particular integrationscheme. The composition and configuration of the layers may be tailoredto provide additional functionality to the SiC-based copper diffusionbarrier film, and therefore to an IMD in which the copper diffusionbarrier film is incorporated. While the dielectric constants of theindividual nitrogen- and oxygen-doped silicon carbide layers isgenerally greater than 4, the much lower dielectric constant of theundoped silicon carbide portion of the barrier film brings its overall k(effective k, k_(eff)) down below 4. In this way, the invention provideseffective low-k IMD/Cu integration schemes. Some examples of thesemulti-layer barrier films are illustrated in FIGS. 2A-2E.

Referring to FIG. 2A, a UDC/ODC bi-layer copper diffusion barrier filmin accordance with one embodiment of the present invention is shown. Thebarrier film 201 is shown disposed on the surface of a copper layer 203,such as a metal line or via, in order to provide some context for howthe film would be disposed when used in a semiconductor device. Thebi-layer film is composed of a layer of UDC 205 on the copper 203 and alayer of ODC 207 on the UDC. When the UDC layer 205 deposited betweenthe freshly reduced Cu surface 203 and the ODC layer 207, it preventsthe freshly reduced Cu surface from being re-oxidized by the ODC layerand promotes adhesion of the SiC film to the copper. The ODC layerblocks moisture absorption.

Since UDC and ODC films contain no amine (NH) source, the film will notcause any via poisoning during dual damascene integration. NDC filmsprovide good etch selectivity to via/line dielectric films due to largecompositional differences and good reliability due to stabilized Si—Nand/or Si—C—N bonding. However, there are concerns that a NH₃-basedprocess and/or a Nitrogen containing plasma based process such as NDCmight result in via poisoning, and NDC films have shown higher k valuesthan that of ODC or UDC films. It has been found that 200 Å or more ofODC or UDC layers are enough to prevent via poisoning no matter thethickness of the NDC layer.

Referring the FIG. 2B, NDC/UDC/ODC tri-layer copper diffusion barrierfilm in accordance with one embodiment of the present invention isshown. The tri-layer film is composed of a layer of NDC 215 on thecopper 203, a layer of UDC on the NDC and a layer of ODC 207 on the UDC.According to this scheme, the NDC layer 213 provides enhanced etchselectivity and the ODC layer blocks moisture absorption. the highcarbon-content UDC layer 215 deposited in between confers low k on theentire stack.

A variety of other multi-layered SiC configurations are illustrated inFIGS. 2C-2E:

FIG. 2C is a bi-layer film 221 that combines a first layer of NDC 225 onthe surface of the copper 223 and a second layer of UDC 227 on the NDC225. FIG. 2D is a bi-layer film that again combines UDC and NDC, butthis time UDC forms the first layer 235 on the surface of the copper 233and NDC the second layer 237 on the UDC. Both of these films combine thelow-k and etch selectivity properties of NDC and UDC to form enhancedlow-k barrier films.

FIG. 2E is a bi-layer film 241 that combines a first layer of NDC 245 onthe surface of the copper 243 and a second layer of ODC 247 on the NDC245. This film combines etch selectivity and moisture barrier propertiesof NDC and ODC to form an enhanced copper diffusion barrier film.Depending on the precursors used and the thicknesses of the layers thisfilm may not have an effective dielectric constant quite as low as thosebarrier films incorporating UDC, but it may nevertheless find use in anumber of integration schemes.

The thickness of each of the stack layer is determined by theapplication needs. The relative thickness of the NDC, ODC and/or UDClayers determines the k and the etch selectivity of the entire stack(k_(eff)). As noted above, the thickness of the film may be from about20 to 2000 Å, for example about 500 Å. The relative thickness of thefilm layers may vary depending on the requirements of the integration.The k values of NDC, UDC, and ODC are precursor dependent and can betuned by the stack combinations according to the overall performanceconsiderations, such as are shown in Table 1, above, and FIGS. 3 and 4,below. In one specific embodiment, a UDC/ODC bi-layer with 150 Å of UDCfollowed by 350 Å of ODC provides a barrier film with k_(eff)<4. Inanother specific embodiment, a NDC/UDC bi-layer with 150 Å of NDCfollowed by 350 Å of UDC provides a barrier film with k_(eff)<3.5.

It has been found that the overall parametric performance for singlelayer and multi-layered barrier film stacks in accordance with thepresent invention is similar. Stress migration performance andelectromigration lifetime is improved with multi-layer SiC barrierfilms.

The step of forming a copper diffusion barrier film involves aplasma-enhanced chemical vapor deposition (“PECVD”) process conducted ina PECVD reactor. Conventional PECVD reactors are suitable forimplementation of the present invention. The PECVD process may involveflowing an organosilicon precursor gas at rates in the range ofapproximately 50 to 2000 standard cubic centimeters per minute and/or aliquid precursor at rates in the range of approximately 0.3-5.0 ml perminute, for example, 0.5-3.0 ml/min, and flowing carrier gas e.g., Heand/or H₂ and/or Ar in the range of approximately 0 to 9000 standardcubic centimeters per minute, for an undoped SiC (UDC) layer. An oxygendoped SiC (ODC) layer may be formed by additionally flowing up to 1000sccm of O₂ and/or other oxygen source, such as CO₂. A nitrogen doped SiC(NDC) layer may be formed by additionally flowing up to 5000 sccm ofnitrogen (N₂), ammonia (NH₃) or other nitrogen source. The PECVD processmay be performed at temperatures in the range of approximately 200 to425° C., at pressures in the range of approximately 0.1 torr to 10 torr(for example about 4-8 torr), at high frequency RF power of about500-3000 W and low frequency RF power at 0-1000 W, and/or at frequenciesin the range of approximately 200 to 500 kHz. Alternatively, the PECVDprocess may be performed at a frequency of approximately 13.56 MHz or 27MHz.

The method may also include a pretreatment for removing copper oxidefrom the copper layer prior to forming the copper diffusion barrier onthe copper layer. The pretreatment may involve exposing the copper layerto ammonia and/or hydrogen gas and/or helium and/or a nitrogen plasma.In some instances, a post-treatment may also be conducted, for example,exposing an oxygen-doped silicon carbide layer to CO₂ gas and/or O₂plasma to condition the surface to optimally block moisture absorption.

Other embodiments of the invention include a wholly or partiallyfabricated semiconductor device. The device includes a metalinterconnect formed substantially of copper and a copper diffusionbarrier adjacent the metal interconnect. The copper diffusion barrier isformed of single or multi-layer silicon carbide films as describedabove. In some such devices, the copper diffusion barrier film may becomposed of a single silicon carbide layer. In other such devices, thecopper diffusion barrier films may be composed of multiple layers ofsilicon carbide having different compositions arranged to achieveeffective low-k IMD/Cu integration schemes, as noted above.

Some aspects of the invention provide a method of forming at least aportion of a semiconductor device according to well known dual damascenefabrication techniques, but using the high carbon-content SiC precursorsand integration schemes according to the present invention. The methodincludes the following steps: forming a trench in a first dielectriclayer; forming a copper interconnect on the in the trench (whichgenerally involves depositing a metal diffusion barrier in the trenchand depositing a copper seed layer on the metal diffusion barrier); andforming a copper diffusion barrier in accordance with the presentinvention on the copper interconnect.

Alternative Embodiments

While the present invention is directed primarily to copper diffusionbarrier films having effective dielectric constants of less than 4, anumber of the multi-layer integration schemes described herein may beuseful as copper barriers, etch stops, etc., in applications in which aneffective dielectric constant of greater then 4 is acceptable, forexample, between 4 and 4.5. Some multi-layer SiC films, particularlythose which do not include undoped SiC, for example some NDC/ODCbi-layers, confer some of the integration benefits of multilayer barrierfilms of the present invention, even if their effective dielectricconstants are not quite as low (i.e., below 4) as those barrier filmsincorporating UDC.

In addition, conventional tetramethylsilane (4MS) precursor may be usedfor one or more layers of a multi-layer film in some instances. In thiscase, the low-k of other high carbon-content layers in the stack (inparticular, a high carbon UDC layer) may compensate for the higher k ofthe material formed by the 4MS (or other relatively low carbon-content)precursor so that the effective k of the film is within the desirablerange.

EXAMPLES

The examples presented here are intended to better illustrate theinvention as described herein and are non-limiting.

Example 1 k_(eff) Simulation in Bi-Layer SiC Structure

FIG. 3 provides a plot of the results of a simulation conducted todetermine the effective dielectric constant of various bi-layer copperdiffusion barrier films in accordance with the present invention.Experimental results are in excellent agreement with the target values,indicating no evidence of process induced damage. For example, 150 ÅNDC/350 Å ODC gives k=3.61 and 150 Å NDC/350 Å UDC and 150 Å UDC/350 ÅODC give k=3.44 and k=3.86, respectively.

Example 2 k and Stress Drift

FIG. 4 provides a plot the relationship between as-deposited and actualdielectric constant (k drift) and stress drift for undoped siliconcarbide copper diffusion barrier films deposited using differentprecursors in accordance with the present invention. The resultsindicate that films formed from ETMS, VPMS and DMPS precursors all havegood k and stress drift performance.

CONCLUSION

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are many alternative waysof implementing both the process and compositions of the presentinvention. For example, while the invention has been described primarilyin terms of preparing integrated circuits, it is not so limited.Accordingly, the present embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalents of the appended claims.

The entire disclosures of all references cited herein are incorporatedby reference for all purposes.

1. A copper diffusion barrier film, for use in a semiconductor device,the copper diffusion barrier film comprising: at least one layer ofundoped carbon-rich silicon carbide, the layer having a composition ofat least 40 atomic % carbon (C) and a dielectric constant of less thanabout 4, wherein the layer is a reaction product of a plasma reaction ofone or more silicon carbide precursors, wherein at least one precursoris selected from the group consisting of ethynyltrimethylsilane,tri-isopropylsilane, 3-(trimethylsilyl)cyclopentene, andvinyldimethylsilane; and one or more additional layers of siliconcarbide forming a stack, wherein at least one of the additional layershas a dielectric constant higher than the dielectric constant of thecarbon-rich silicon carbide, wherein the diffusion barrier film has aneffective dielectric constant of less than about 4.5.
 2. The copperdiffusion barrier film of claim 1, wherein the film has an effectivedielectric constant of less than about 4.0.
 3. The copper diffusionbarrier film of claim 1, wherein the film has a thickness from about 20to 2000 Å.
 4. The copper diffusion barrier film of claim 1, wherein thefilm has a thickness of about 500 Å.
 5. The copper diffusion barrierfilm of claim 1, wherein the layer of undoped carbon-rich siliconcarbide resides in contact with a copper line.
 6. The copper diffusionbarrier of claim 1, wherein the carbon-rich silicon carbide has a C toSi ratio of greater than 4:1.
 7. The copper diffusion barrier film ofclaim 1, wherein the undoped carbon-rich silicon carbide layer contactsa copper line, and wherein the film comprises an oxygen doped siliconcarbide layer stacked upon the carbon-rich silicon carbide layer.
 8. Thecopper diffusion barrier film of claim 1, comprising a layer ofnitrogen-doped silicon carbide contacting a copper line, wherein thelayer of undoped carbon-rich silicon carbide is stacked upon the layerof nitrogen-doped silicon carbide.
 9. The copper diffusion barrier filmof claim 1, wherein the undoped carbon-rich silicon carbide layercontacts a copper line, and wherein the film comprises a nitrogen-dopedsilicon carbide layer stacked upon the carbon-rich silicon carbidelayer.
 10. A copper diffusion barrier film, for use in a semiconductordevice, the copper diffusion barrier film comprising: at least one layerof doped carbon-rich silicon carbide, the layer having a composition ofat least 40% atomic carbon (C) and a dielectric constant of less thanabout 4, wherein the layer is a reaction product of a plasma reaction ofone or more silicon carbide precursors, wherein at least one precursoris selected from the group consisting of ethynyltrimethylsilane,tri-isopropylsilane, 3-(trimethylsilyl)cyclopentene, andvinyldimethylsilane; and one or more additional layers of siliconcarbide forming a stack, wherein at least one of the additional layershas a dielectric constant higher than the dielectric constant of thecarbon-rich silicon carbide, wherein the diffusion barrier film has aneffective dielectric constant of less than about 4.5.
 11. A copperdiffusion barrier film, for use in a semiconductor device, the copperdiffusion barrier film comprising: at least one layer of carbon-richsilicon carbide, the layer having a composition of at least 40 atomic %carbon (C) and a dielectric constant of less than about 4, wherein thelayer is a reaction product of a plasma reaction of one or more siliconcarbide precursors, wherein at least one precursor is selected from thegroup consisting of ethynyltrimethylsilane, tri-isopropylsilane,3-(trimethylsilyl)cyclopentene, and vinyldimethylsilane.
 12. A copperdiffusion barrier film, for use in a semiconductor device, the copperdiffusion barrier film comprising: at least one layer of undopedcarbon-rich silicon carbide, the layer having a composition of at least40 atomic % carbon (C) and a dielectric constant of less than about 4;and one or more additional layers of silicon carbide forming a stack,wherein at least one of the additional layers has a dielectric constanthigher than the dielectric constant of the carbon-rich silicon carbide,wherein the diffusion barrier film has an effective dielectric constantof less than about 4.5, wherein the undoped carbon-rich silicon carbidelayer contacts a copper line, and wherein the film comprises anoxygen-doped silicon carbide layer or a nitrogen-doped silicon carbidelayer stacked upon the carbon-rich silicon carbide layer.
 13. The copperdiffusion barrier film of claim 12, wherein the undoped carbon-richsilicon carbide layer contacts a copper line, and wherein the filmcomprises an oxygen doped silicon carbide layer stacked upon thecarbon-rich silicon carbide layer.
 14. The copper diffusion barrier filmof claim 12, wherein the undoped carbon-rich silicon carbide layercontacts a copper line, and wherein the film comprises a nitrogen-dopedsilicon carbide layer stacked upon the carbon-rich silicon carbidelayer.